Gunnar Nævdal

The interaction of temperature and salinity on growth and food conversion in juvenile turbot (Scophthalmus maximus)

Abstract The effects of temperature and salinity on growth and feed conversion of juvenile turbot (initial mean weight 14 g) were investigated by rearing fish at (mean±SD) 10±0.2°C, 14±0.2°C, 18±0.3°C and 22±0.2°C and 15±0.4‰, 25±0.4‰ and 33.5±0.1‰ for 3 months. Growth, food consumption, and food conversion efficiency were highest at 15‰, and lowest at 33.5‰. There was an interactive effect of temperature and salinity at the two highest temperatures (18°C and 22°C) but not at 10°C and 14°C. The optimal temperature for growth (Topt. G) varied with salinity: Topt. G at 33.5‰ was 19.6±0.3°C (±SEM), whereas the Topt. G at 15‰ was 22.9±1.0°C, and at 25‰ was 24.7±2.1°C. A similar trend was found for food conversion efficiency (FCE). The optimal temperatures for FCE were 17.4±0.5°C, 17.9±1.0°C and 19.0±0.9°C at 33.5‰, 25‰ and 15‰, respectively. Overall, we found the optimal temperature–salinity combination for growth to be 21.8±0.9°C and 18.5±0.8‰. The optimal temperature–salinity combination for food conversion efficiency was found to be 18.3±0.6°C and 19.0±1.0‰. It is concluded that growth and food conversion efficiency of juvenile turbot can be improved by rearing them at intermediate salinities in the upper temperature range.

Genetic factors in connection with age at maturation

Abstract Age at first maturation is an important economic characteristic for farming of Atlantic salmon and rainbow trout because the maturation process retards and even stops the growth rate for several months, and often causes increased mortality. In the present paper causes of variation in age at first maturation are dealt with. Literature on this topic is briefly reviewed, and experiments carried out at the Institute of Marine Research, Bergen, are reported. The influence of genetic factors seems clear. However, ecological factors affecting condition or growth rate of the fish seem also to be involved. Interdependence between age of maturation and size was found within families, although no minimum size need be attained before the maturation process starts. Differences between 1- and 2-year smolts were noted. Genetic variation in incidences of precocious maturation seems to exist, but no clear connection was found between this trait and maturation later on in the sea. The significance of precocious maturation for fish farming seems still obscure.

Pigmentation of salmonids — Genetical variation in carotenoid deposition in rainbow trout

Significant differences in the carotenoid, astaxanthin and cantaxanthin levels were observed between full-sib and half-sib of rainbow trout (Salmo gairdneri). The sex did not affect pigment deposition but a weak negative correlation between fish weight and level of carotenoids in the flesh was found.

Pigmentation of salmonids — Variation in flesh carotenoids of Atlantic salmon

Abstract The aim of the present study was to determine some causes of variation in pigmentation of Atlantic salmon ( Salmo salar ) reared under commercial conditions. At slaughter of one year class of Atlantic salmon, composed of half-sib and full-sib groups, the levels of carotenoids in flesh and ovaries were determined. it was found that the level of carotenoid was influenced by the genetic background of the fish, the stage of sexual maturation and weight. The relative importance of each of these factors is discussed.

Growth rate related to genotype of 0-group cod at three environmental temperatures

Abstract Growth rates of cod of an initial weight of about one gram were studied at three environmental temperatures (6, 10, and 14° C) for about 70 days. Samples of all three groups of fish were genotyped for haemoglobin and several tissue enzymes by agar or starch gel electrophoresis. Size at termination of the experiment, regarded to represent individual growth rate, was studied separately for frequent genotypes within temperature groups. No clear associations between mean growth rate and genotypes of the enzymes LDH or PGI were found at any temperature. However, fish of the genotype Hb-I(2/2) showed the highest mean growth rate regardless of environmental temperature, and fish of genotype Hb-1(1/1) grew on average slowest at the two higher temperatures. This observation was partly in contrast to earlier findings indicating that the performance of the different genotypes is temperature dependent, with Hb-1(2/2) as the more efficient at lowest temperatures.

Genotype distributions of cod from the Norwegian Skagerrak coast

Abstract The genotype distributions for cod, Gadus morhua L., from the southeastern coast of Norway are studied as part of a more extensive study on cod enhancement and the possible effects of mass liberation of 0-group cod on endemic cod populations. This paper focus on possible geographical variation in allele frequencies, temporal variations in haemoglobin type frequencies and mean length of age of various genotypes. Twelve samples were analysed for genotype distribution of haemoglobins and the tissue enzymes LDH, PGI, IDH, PGM, and GPD by agar-gel and starch gel electrophoresis. Some inters ample variations were found indicating heterogeneity of the total cod stock structure in the area. The haemoglobin-controlling genes occurred with similar frequencies in this material as in corresponding material analysed more than 25 years earlier. Possible associations between life history traits and individual genotypes were investigated, and genotype-dependent growth rate was indicated.

Microsatellite variation in populations of Atlantic salmon from North Europe

Our aim was to investigate the level of genetic differentiation in northern European populations of Atlantic salmon, to establish the genetic relationship among major salmon populations in Russia and North Norway, and to compare these to populations from the western Atlantic lineage. Samples were collected along an east—west axis, from Pechora River in Russia to Restigouche River in Quebec, Canada. A total of 439 individual salmon were collected from seven rivers (sample sizes from 50 to 84 individuals). The samples were analysed for variation at four microsatellite loci; Ssa13.37, Ssa14, Ssa171 and Ssa171. Significant differences were found between most of the European populations, and the populations from the Tana and Pechora Rivers were most distinct. The samples from the Rivers Mezenskaya Pizhma and Emtsa in Arkhangelsk oblast in Russia were not significantly different from each other in an exact test of population differences. All other river pairs were significantly different. These results confirmed the deep genetic divergence between American and European salmon populations demonstrated in earlier studies, with alleles specific to continent found in three of the microsatellites.

Variations in growth in haemoglobin genotypes of Atlantic cod

In the present paper are described the growth properties of three different haemoglobin genotypes of juvenile Atlantic cod (Gadus morhua) reared at 7, 10, 13 and 16 °C. In addition one group was reared under “temperature steps” i.e. moved successively from 16 to 13 and 10 °C. The genotype Hb-I(2/2)displayed the overall highest growth rate in the temperature range 13–16 °C, whereas the Hb- I(1/1)genotype showed the highest overall growth at the lowest temperature (7 °C). Accordingly, we found a significant interaction between genotype and temperature. The differences in growth were largest when cod were reared under the temperature step regime where the Hb-I(2/2)genotype displayed 17 and 24% higher growth than Hb-I(1/1)and Hb-I(1/2),respectively. Optimal temperature for growth (Topt.G) varied between the genotypes with the genotype Hb-I(1/2)displaying the highest (mean ± SE) Topt.G (14.5 ± 1:0.8 °C) and Hb-I(1/1)the lowest (12.5 ± 0.2 °C). The biological significance of this link between biochemical genetic variation and physiological properties might be the influences on growth pattern, ultimate size and age at first maturity.

Selection or adaptation: Differences in growth performance of juvenile turbot (Scophthalmus maximus Rafinesque) from two close-by localities off Norway

Abstract Growth perfonnance was investigated in two populations of juvenile turbot (Scophthalmus maximus Rafinesque) from two close-by localities on the Norwegian coast, both caught at the southwest coast and called SW1 and SW2, reared together under four different temperature regimes. All growth indices showed that the growth performance of the SW1 Norwegian population was superior compared to the SW2 Norwegian population especially at the extreme temperatures. Our findings may indicate local adaptation of turbot. We discuss if local adaptation will be reflected in neutral genetic markers as the variation in growth is higher than the genetic variability previously reported for this species, which might make the non-neutral markers a better tool to understand local adaptation of fish populations. Alternatively our results could indicate hatchery selection or a strong genetic drift which may cause a substantial genetic change eventually leading to inbreeding depression which again may cause decreased growth.

Haemoglobin variation in cod: a description of new variants and their geographical distribution

Blood from 1209 individual cod was sampled from nine localities in the Northeast Atlantic, and analysed using agar gel electrophoresis (AGE) and isoelectric focusing (IEF) to reveal individual and population variation in haemoglobin genotypes. The second aim of the study was to compare our data with data collected some 30 years ago in the same area to investigate possible directional selection. A new haemoglobin polymorphism of Atlantic cod was documented in samples from Danish waters using IEF electrophoresis (pH 5.5-8.5) and, in addition to the five genotypes seen in earlier studies, 11 subtypes are described. Significantly different genotype distributions were found between the samples from northern Norway on the one hand and southern Norway and Danish waters on the other, and the frequency of the Hb-I(1) allele increased from north to south. With the possible exception of two samples, the frequency of the main haemoglobin genotypes was found to be very similar to corresponding frequencies described in these areas three decades ago. The frequencies of the Hb-I subtypes off Norway varied among the sampling sites and were only found in Norwegian coastal cod with increasing frequency from north to south. In the Danish samples, 11 novel Hb-I subtypes were found and are described.